U.S. patent number 10,995,037 [Application Number 16/218,881] was granted by the patent office on 2021-05-04 for high temperature composite structure and system for detecting degradation thereof.
This patent grant is currently assigned to United States of America as represented by the Secretary of the Air Force. The grantee listed for this patent is Government of the United States, as represented by the Secretary of the Air Force, Government of the United States, as represented by the Secretary of the Air Force. Invention is credited to Zlatomir D. Apostolov.
United States Patent |
10,995,037 |
Apostolov |
May 4, 2021 |
High temperature composite structure and system for detecting
degradation thereof
Abstract
The present disclosure includes a system and method for
monitoring degradation of a high temperature composite component
(HTC). The HTC is defined by a volume that includes a matrix
material and a fiber formed from at least one of ceramic and carbon
material. One or more electrical conductors are disposed within the
volume and connected directly or indirectly to a monitoring
system.
Inventors: |
Apostolov; Zlatomir D.
(Beavercreek, OH) |
Applicant: |
Name |
City |
State |
Country |
Type |
Government of the United States, as represented by the Secretary of
the Air Force |
Wright-Patterson AFB |
OH |
US |
|
|
Assignee: |
United States of America as
represented by the Secretary of the Air Force (Wright-Patterson
AFB, OH)
|
Family
ID: |
1000003821187 |
Appl.
No.: |
16/218,881 |
Filed: |
December 13, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C04B
35/62231 (20130101); C04B 35/62272 (20130101); C04B
2235/5256 (20130101); C04B 2235/5288 (20130101); C04B
2111/94 (20130101); C04B 2235/522 (20130101); C04B
2235/40 (20130101); C04B 2235/5248 (20130101) |
Current International
Class: |
C04B
35/622 (20060101) |
Field of
Search: |
;252/511 ;313/309 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
2570117 |
|
Jan 2014 |
|
CA |
|
108426919 |
|
Aug 2018 |
|
CN |
|
2180940 |
|
Sep 1989 |
|
GB |
|
2000321169 |
|
Nov 2000 |
|
JP |
|
101781687 |
|
Sep 2017 |
|
KR |
|
2013086626 |
|
Jun 2013 |
|
WO |
|
Other References
Ciang et al., "Structural health monitoring for a wind
turbinesystem: a review of damage detection methods," 2008 Meas.
Sci. Technol. Dec. 19, 2001. cited by applicant .
Kessler et al., "Damage detection in composite materials usingLamb
wave methods," 2002 Smart Mater Struct. 11 269. cited by applicant
.
Masters et al., "Damage Detection in Composite Materials," ASTM,
Aug. 1992. cited by applicant .
Matsuzaki et al., "Wireless detection of internal delamination
cracks in CFRPlaminates using oscillating frequency changes,"
Composites Science and Technology 66 (2006) 407-416. cited by
applicant .
Pandey et al., "Damage Detection From Changes in Curvaturemode
Shapes," Journal of Sound and Vibration (1991) 145(2), 321-332.
cited by applicant .
Zhou et al. "Damage detection and assessment in fibre-reinforced
composite structures with embedded fibre optic sensors--review,"
Smart Mater.Struct. 11 (2002) 925-939. cited by applicant .
Zhou et al., "Damage detection and assessment in fibre
reinforcedcomposite structures with embedded fibre optic
sensors--review," 2002 Smart Mater. Struct. 11 925. cited by
applicant .
Zou, et al., "Vibration-Based Model-Dependent Damage(Delamination)
Identification and Healthmonitoring for Composite Structures--A
Review," Journal of Sound and Vibration (2000) 230 (2), 357-378.
cited by applicant.
|
Primary Examiner: Nguyen; Khanh T
Attorney, Agent or Firm: AFMCLO/JAZ Fair; Matthew D.
Government Interests
GOVERNMENT RIGHTS STATEMENT
The invention described herein may be manufactured and used by or
for the Government of the United States for all governmental
purposes without the payment of any royalty.
Claims
What is claimed is:
1. A high temperature composite (HTC) having a volume comprising: a
matrix material comprising at least one of ceramic and carbon,
fiber comprising at least one of ceramic and carbon, the fiber
dispersed within the matrix material, electrical conductors; and
wherein the electrical conductors comprise metal wires formed as
staples buried at different depths of the HTC.
2. The HTC of claim 1, wherein the electrical conductors comprise
electrically conductive surface coatings on a portion of the
fibers.
3. The HTC of claim 1, wherein the electrical conductors comprise
metal wires disposed in a parallel orientation.
4. The HTC of claim 1, wherein the electrical conductors comprise
metal wires disposed in a grid orientation.
5. The HTC of claim 1, wherein portions of the electrical
conductors extend outside of the volume.
6. The HTC of claim 1, wherein the electrical conductors are wholly
contained within the volume.
7. The HTC of claim 1, wherein the electrical conductors comprise
at least one of niobium, molybdenum, tantalum, tungsten, rhenium,
titanium, vanadium, chromium, zirconium, hafnium, ruthenium,
rhodium, osmium iridium, and platinum.
8. The HTC of claim 1, wherein the HTC comprises at least one of a
surface, structural, propulsion, and functional component of an
aircraft that is exposed to an aggressive environment.
9. The HTC of claim 1, wherein the fibers comprise plies of woven
fibers.
10. The HTC of claim 1, wherein the fibers comprise plies of
nonwoven webs of fibers.
11. A high temperature composite (HTC) having a volume comprising:
a matrix material comprising at least one of ceramic and carbon,
fiber comprising at least one of ceramic and carbon, the fiber
dispersed within the matrix material, electrical conductors; and
wherein portions of the electrical conductors extend outside of the
volume.
12. The HTC of claim 11 wherein the electrical conductors comprise
metal wires are disposed in at least one of a parallel orientation
and/or a grid orientation.
Description
FIELD OF THE INVENTION
This invention relates to the field of high temperature ceramic or
carbon composites. More particularly, this invention relates to
detecting the structural integrity of components made from such
materials.
BACKGROUND OF THE INVENTION
The manufacturing process for a high temperature composite (HTC)
typically consists of (1) lay-up and fixation of the fibers, shaped
as the desired component (as used herein, the term lay-up also
includes a preform, as described in more detail hereafter), (2)
infiltration of the matrix material, and (3) curing and firing of
the HTC to drive off volatile compounds, leaving just the HTC
material remaining, namely fiber and matrix, with the latter being
ceramic or carbon-based. The first and second steps can be
iteratively repeated by performing a partial cure after each
fixation and infiltration of a fiber ply, then fixing, infiltrating
and partially curing another ply, and so forth until the component
is completed, and then firing the entire component.
In the first step, the fibers are arranged and fixed such as by
lay-up of fabrics, winding, braiding, knotting, or by the formation
of a three-dimensional preform. In the case of a preform, plies are
stacked up and sequentially needled in the through-thickness
direction to provide improved inter-laminar properties. Each of
these layers is referred to as a ply herein. The end result of
fixing a plurality of these plies is called a preform. Many
different options are available for the second step of matrix
formation, such as deposition out of a gas mixture, pyrolysis of an
infiltrated pre-ceramic polymer, chemical reaction of molten
metallic precursors, and electrophoretic deposition of a ceramic
powder. These are usually followed by sintering and crystallization
at temperatures of between about 1000.degree. C. and 1700.degree.
C.
As used herein, the term high temperature composites (HTCs) refers
to composites where both the fibers and the matrix are at least one
of ceramic based and carbon based. Such HTCs are used to form
components that are deployed in extreme environments, such as high
temperature, high stress, or high corrosion. Other types of
composites, such as polymer matrix composites (PMCs), typically
cannot survive for any reasonable length of time in these
environments.
PMCs are also formed at much lower temperatures than HTCs, at less
than about 500.degree. C., whereas HTCs are generally fabricated at
temperatures greater than about 1100.degree. C. Thus, the materials
and methods that are applicable to PMCs are not applicable to
HTCs.
Because HTC components are exposed to such extreme environments,
they need to be inspected at regular intervals to detect any
structural degradation. In the absence of such inspections, a
component might fail, leading to catastrophic damages. Some of the
structural problems that can occur are spalling, cracking, chemical
reaction, and erosion (ablation).
However, removing such a component from use to perform the
inspection can be expensive and time consuming. Further, in some
applications it can be useful to monitor any degradation of the
component in real time, as it is being used.
What is needed, therefore, are structures and methods that tend to
reduce the issues suggested above, at least in part.
SUMMARY OF THE INVENTION
These and other needs are met by a HTC having a volume that
includes a matrix material of at least one of ceramic and carbon,
fiber of at least one of ceramic and carbon, where the fiber is
dispersed within the matrix material, and electrical
conductors.
In some embodiments according to this aspect of the invention, the
electrical conductors include electrically conductive surface
coatings on a portion of the fibers. In some embodiments, the
electrical conductors include metal wires disposed in a parallel
orientation. In some embodiments, the electrical conductors include
metal wires disposed in a grid orientation. In some embodiments,
the electrical conductors include metal wires formed as staples
buried at different depths of the HTC.
In some embodiments, portions of the electrical conductors extend
outside of the volume. In some embodiments, the electrical
conductors are wholly contained within the volume. In some
embodiments, the electrical conductors include at least one of
niobium, molybdenum, tantalum, tungsten, rhenium, titanium,
vanadium, chromium, zirconium, hafnium, ruthenium, rhodium, osmium
iridium, and platinum. In some embodiments, the HTC is at least one
of a surface, structural, propulsion, and functional component of
an aircraft that is exposed to an aggressive environment. In some
embodiments, the fibers are plies of woven fibers. In some
embodiments, the fibers are plies of nonwoven webs of fibers.
According to another aspect of the invention, there is described a
HTC having a volume including a matrix material comprising at least
one of ceramic and carbon. The matrix material has a first
conductive portion and a second nonconductive portion, where the
first portion and the second portion are substantially
non-intermixed. The volume also includes fiber that includes at
least one of ceramic and carbon, where the fiber is dispersed
within the matrix material.
In some embodiments according to this aspect of the invention, the
first portion is disposed in a same position throughout a depth of
the volume, while in other embodiments, the first portion is
disposed in multiple positions throughout a depth of the volume,
where the first portion disposed at one position in the depth does
not contact the first portion disposed in another position in the
depth. In some embodiments, the first portion is comprised of the
second portion plus conductive additives comprising at least one of
refractory metallic particulate and electrically conductive
carbon-based material having at least one of graphene and
nanotubes. In some embodiments, the HTC comprises at least one of a
surface, structural, propulsion, and functional component of an
apparatus that is exposed to an aggressive environment. In some
embodiments, the fiber comprises plies of woven fibers. In some
embodiments, the fiber comprises plies of a nonwoven web of
fibers.
According to another aspect of the invention there is described a
method for monitoring degradation of a HTC component, where the HTC
component as provided includes a volume of a matrix material that
includes at least one of ceramic and carbon, and fiber that
includes at least one of ceramic and carbon, where the fiber is
dispersed within the matrix material. Electrical conductors are
also included within the volume. Electrical properties of subsets
of the electrical conductors are monitored, and a report is
provided when the electrical properties of a given subset of the
electrical conductors crosses a predetermined threshold. The HTC
component is selectively remediated based on the report.
In various embodiments according to this aspect of the invention,
the HTC is at least one of a surface, structural, propulsion, and
functional component of an apparatus that is exposed to an
aggressive environment.
BRIEF DESCRIPTION OF THE DRAWINGS
Further advantages of the invention are apparent by reference to
the detailed description when considered in conjunction with the
figures, which are not to scale so as to more clearly show the
details, wherein like reference numbers indicate like elements
throughout the several views, and wherein:
FIG. 1 is a perspective view of a HTC with electrical leads
according to a first embodiment of the present invention.
FIG. 2 is a perspective view of a HTC with electrical leads
according to a second embodiment of the present invention.
FIGS. 3A and 3B are views of a HTC with electrical leads according
to a third embodiment of the present invention.
FIG. 4 is a perspective view of a HTC with an electrically
conductive portion according to a fourth embodiment of the present
invention.
FIG. 5 is a perspective view of a HTC with electrically conductive
portions according to a fifth embodiment of the present
invention.
FIG. 6 is a perspective view of a HTC with embedded electrically
conductive structures according to a sixth embodiment of the
present invention.
FIG. 7 is a perspective view of a HTC with embedded electrically
conductive structures according to a seventh embodiment of the
present invention.
FIG. 8 is a functional block diagram of an apparatus that uses an
HTC according to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
General Overview
According to various embodiments of the present invention, there is
added an electrically conductive system to the lay-up, such as by
modifying portions of the matrix to be electrically conductive or
by adding electrically conductive structures to or between the
plies. In some embodiments the electrically conductive system spans
the entire ply in which it is formed, with a plurality of
conductive members individually formed in or between a plurality of
the plies.
In some embodiments the electrically conductive system can be
monitored in-situ or ex-situ, and in other embodiments the
electrically conductive system can only be monitored ex-situ.
Because the electrically conductive system is disposed at multiple
layers through the component, the degree of cracking, abrasion,
corrosion, and ablation (all generally referred to as wear herein)
to the component can be monitored. Because the electrically
conductive system extends, at least in some embodiments, across an
entire ply in which it is disposed, the location and depth of such
wear can be monitored.
SPECIFIC EMBODIMENTS
With reference now to the figures, various specific embodiments of
the present invention are described.
FIG. 1 depicts a lay-up 100 according to an embodiment of the
present invention, with five plies 102 that have been infiltrated
with a matrix 106. FIG. 1 and the other figures are highly
representational, in that they show a top-most ply 102 curled back
so as to reveal the electrical conductors 104 that are disposed
either within an underlying ply 102 or between two adjacent plies
102. The number of plies 102 in the lay-up 100 is representational
only, and not limiting. So too the number, shape, location, and
depth of the electrical conductors 104 as depicted is
representational only and not limiting.
In the embodiment of FIG. 1, the electrical conductors 104 take the
form of electrically conductive wires that come up through the
bottom of the lay-up 100 to one or more of a plurality of different
levels and positions, in a configuration that generally resembles a
staple. By placing these staples in positions that cover the
length, width, and depth of the lay-up--meaning from side to side,
front to back, and between all of the plies 102, the position and
depth of any wear that the lay-up 100 might incur can be
monitored.
For example, the ends of the electrical conductors 104 can be
connected to an instrument such as a conductivity meter, and the
conductivity of each of the individual conductors 104 can be
monitored. A crack in one position of the lay-up 100 will tend to
sever an electrical conductor 104 that is disposed in that
position, and the associated loss of conductivity through the
electrical conductors 104 will be detected by the instrument, and
can be reported to a controller, such as an on-board computer.
Thus, the computer can track the position and depth of wear within
a given component of the apparatus (aircraft, vehicle, etc.) that
is constructed in this manner.
In a similar manner, as plies 102 are ablated away from the
component due to heat, friction, corrosion and other factors,
electrical conductors 104 will start to become open circuits at
levels that are deeper and deeper within the lay-up 100, and in
this manner the computer can monitor the rate at which wear is
occurring within the lay-up 100. Thus, both the position and the
depth of wear can be monitored in-situ or ex-situ.
FIG. 2 provides a depiction of a different structure for the
electrical conductors 104, in which they form an array of crossing
electrical leads that are disposed either within or between various
layers of the plies 102. In some embodiments, the wires forming the
electrical conductors 104 extend to the edge of the lay-up 100, and
are electrically connected to an instrument, such as a conductivity
meter as described above. In some embodiments the lateral positions
of the wires of the electrical conductors 104 are offset from one
layer to the next, so as to provide more finely resolved position
information as electrical conductors 104 are damaged and reported
as open circuits.
FIGS. 3A and 3B depict various ways in which the electrical
conductors 104 can be formed or disposed within a ply 102. In FIG.
3A, electrical conductor 104a is a modified fiber or fiber tow 108
(as described in regard to FIG. 3B), electrical conductor 104b is
laid on top of the ply 102, and electrical conductor 104c is woven
into the ply 102. Alternately, electrical conductor 104a can
replace a fiber 108. In FIG. 3B, the surface of a fiber 108 of the
ply 102 has received a modification that causes a portion 110 of
the fiber 108 to be electrically conductive. This can be
accomplished with the use of a surface treatment, such as a
metallic coating, or by some other means. Either just a portion of
or the entirety of the fiber 108 can have the surface modification
110.
FIG. 4 depicts an embodiment where a portion 112 of the matrix 106
is modified to be electrically conductive, such as by adding an
electrically conductive component to the material of the matrix
106. In the embodiment depicted in FIG. 4, the electrically
conductive portion 112 of the matrix 106 is infiltrated down
through all of the plies 102 in the lay-up 100. In this embodiment,
the degree and position of wear can be detected by monitoring the
reduction of electrical conductivity within a given strip of the
modified portion 112. Thus, the portion 112 serves as the
electrical conductors 104.
In the embodiment of FIG. 5, the electrically conductive portion
112 is only disposed on or in some of the plies 102, such as every
other ply 102. In this embodiment, the degree and position of wear
can be detected by monitoring both the loss and reduction of
electrical conductivity within the strips of the modified
electrically conductive portion 112 that serve as the electrical
conductors 104 at different depths within the lay-up 100. It is
appreciated that the width and number of the modified portions 112
as depicted in FIGS. 5 and 6 is representational and not limiting.
These embodiments can be monitored either in-situ or ex-situ.
FIG. 6 depicts an embodiment where the electrical conductors 104,
such as wires, are disposed within or between various ones of the
plies 102, but are not connected one to another, and which in some
embodiments do not extend outside of the internal portions of the
lay-up 100. In this embodiment the wear that might be sustained by
a given electrical conductor 104 can be detected such as with an
eddy current meter, or some other inductive device. This embodiment
can also provide both in-situ and ex-situ monitoring, but in some
embodiments it is better suited for ex-situ monitoring.
FIG. 7 depicts another embodiment, similar to that as described in
regard to FIG. 6 above, but where the electrical conductors 104 are
formed with a shape that provides passive RF signaling, and thus
can be monitored using radio frequency means either in-situ or
ex-situ. Currently, no embedded RF capability exists for HTCs, and
therefore this embodiment can provide a unique pattern-based
signature for both inspection and communication purposes.
The characteristics of any such antenna design would depend upon
the vehicle type and mission goals, but in one embodiment would be
targeted towards long range and very long range trajectories, which
are generally covered by a frequency range of from about 300 MHz to
about 30 GHz. These in turn correspond to wavelengths of from about
one centimeter to about one meter, typically using antenna elements
(electrical conductors 104) with dimensions that are from about two
to about four times smaller, which is very reasonable to accomplish
through the proposed embodiment.
The location and shape of the electrical conductors 104 would also
be vehicle and mission dependent, but since the proposed method
does not constrain or modify established manufacturing practices,
it allows significant flexibility to integrate the antenna
(electrical conductors 104) at whatever locations are deemed
appropriate. Connectivity of the embedded element (electrical
conductors 104) to the receiver located in the vehicle interior can
be achieved by an additional through-thickness conductor as
described elsewhere herein, which can be part of the initial
antenna structure, or added subsequently during the composite
lay-up, but before solidification of the matrix material of the
composite.
From a non-operational maintenance perspective, a different kind of
embedded antenna (electrical conductors 104) can also be used for
radio frequency identification, and more specifically as a passive
RFID tag to identify individual components of the larger composite
structure. To avoid complicating the system architecture, and
because these types of readouts can be done in ambient
environments, the antenna and the integrated circuit linked to it
can be placed away from critical structural areas, while still
being easily accessible in a maintenance depot environment, for
example. The choice of passive instead of active RFID further
simplifies the design and integration method. One embodiment could
be intended for a frequency range of about 10 MHz to about 15 MHz,
with a readout distance of from about 1 m to about 2 m.
With reference now to FIG. 8, there is depicted a functional block
diagram of a system 800 that can be used to monitor and report on
the condition of an HTC component 802. The HTC component 802 is
formed according to one or more of the embodiments described above,
and is put into service in an apparatus 804, such as an aircraft or
vehicle as generally described herein. Although the component 802
can be used for any part of the apparatus 804, it is particularly
well-suited for a part that is exposed to an extreme environment,
such as discussed elsewhere herein.
In various embodiments, the integrity of the component 802 can be
monitored by a monitor 806 either while the apparatus 804 is in use
(in situ) or when the apparatus 804 is not in use (ex situ). In
various embodiments the monitor 806 takes many different forms,
such as an eddy current meter, RFID reader, or resistometer. In
some embodiments the monitor 806 is directly wired to portions of
the electrical conductors 104 that extend outside of the volume of
the HTCs component 802, and in other embodiments the monitor 806 is
able to sense the extent of any damage to the electrical conductors
104 wirelessly, both as described elsewhere herein.
In some embodiments the monitor 806 is under the control of or
provides readings to a controller 808, such as a computer. In some
embodiments the controller 808 has the monitor 806 scan the entire
component 802, and in other embodiments the controller 808 has the
monitor 806 scan only portions of the component 802, such as if
quickly-evolving damage is occurring to those portions of the
component 802. In some embodiments the controller 808 has the
monitor 806 inspect the component 802 in predetermined locations at
predetermine intervals.
In some embodiments the readings gathered by the monitor 806 are
stored in a memory 810 and can be sent to a remote source 814 such
as via input/output 812, which in some embodiments is operable to
receive instructions from the remote source 814 and apply them to
the controller 808. In some embodiments the controller 808 analyzes
readings from the monitor 806, such as by comparing them to
predetermined values stored in the memory 810. If the readings do
not favorably compare to the stored values, then the controller 808
can send a report, such as signaling an alarm, either through an
interface 816 or to the remote source 814 through the I/O 812. In
some embodiments the remote source 814 makes such comparisons.
ADDITIONAL DESCRIPTIONS
Various embodiments of the present invention integrate electrical
conductors 104, such as refractory metal wires or other
high-temperature materials, within the structure of a HTC. This
ensures that the electrical conductors 104 survive the fabrication
of the HTC, retains its signal generation and transmission
capabilities, and does not negatively affect the properties of the
HTC.
In this manner, users will be able to more accurately evaluate the
in-situ in-flight state of the components made out of the HTCs.
This will lead to a more accurate estimation of the lifetime of the
component with respect to the remaining flight path, and an ability
to optimize its performance based on knowledge of the component's
status. This can have a direct influence on the survivability of
the entire aircraft (as, for example, hypersonic platforms are
often critically dependent on certain hot-structure components),
and ultimately impact the mission outcome.
Potential commercial uses of the invention include various
applications within the aerospace industry, such as vehicle outer
shells, leading edges, high or low acreage thermal protection
systems, engine components, exhausts, hot flow-path components,
missile cones, and so forth, and the power generation industry,
such as land-based gas turbines, and nuclear power generation.
In various embodiments, the invention is incorporated into any
high-temperature ceramic or carbon-based HTC material component,
and is therefore widely applicable. The design can vary according
to the geometry, complexity, composition, expected environment
severity, operational rigor, and degree of required awareness for
the component.
The teachings of the present disclosure provide means, methods and
systems for providing an awareness of the structural and
compositional state of HTC-based components, before, during and
after exposure to aggressive environments. It addresses the problem
of uncertain component lifetime in environments that are extremely
difficult and expensive to replicate in laboratory or industrial
conditions. It provides real-time structural performance
information for the component, which can be used to optimize the
behavior of the supported overall structure. It also allows a means
of evaluating the quality of as-processed HTC components, as well
as their state after operational exposure.
Various applications include, but wouldn't be limited to, outer
body shells of hypersonic vehicles (especially hot surfaces),
internal hot sections of hypersonic vehicles (scramjet/ramjet
engines, intake ducts, flow-path components, and so forth),
conventional turbine engine components, land-based power
generators, smelting operations, and generally any application that
requires structural and compositional performance in high
temperatures and aggressive chemical environments.
One embodiment includes integration of electrical conductors 104 of
refractory metal wires within the HTC, and more specifically
between (or within) the plies 102 of ceramic fiber weave for a
two-dimensional lay-up 100. There are various wire geometries and
integration approaches possible, with two of the less complex ones
shown in the figures. As the HTC component encounters a highly
aggressive environment (such as atmospheric re-entry, atmospheric
flight at hypersonic or near-hypersonic speeds, turbine or
scramjet/ramjet combustion environments, and so forth), the outer
HTC plies 102 are worn away, which subsequently leads to the
degradation and destruction of the electrical conductors 104. The
interruption of each layer of the electrical conductors 104 is
detected by the changes in the signals that they carry, and
therefore provide a measure of detectable progress of the erosion
front, and from there an estimate on the state of the
component.
Another embodiment includes modified native phases of one or more
components of the HTC, such as the matrix 106, fibers 108, or fiber
coatings 110, instead of the introduction of an entirely new phase
(the metal wires as described above). These modifications result in
areas of the matrix 106, fiber 108, or fiber coating 110 that have
properties that are different than those of the surrounding
environment (higher electrical conductivity, for example). In this
manner, components of the HTC itself serve as the sensors. As
before, the sequential degradation of these selectively-modified
HTC regions leads to interruption of the signal going through them,
thus providing an ability to track the progress of the erosion
front.
Yet another embodiment of the invention includes layers of
electrical conductors 104 that are placed between each ply 102 of
the HTC, resulting in a multi-layered sandwich-type structure,
albeit with a miniscule proportion of metallic content.
The wire integration can be completed either before infiltration of
the preform (however the preform is shaped), or after individual
layers have been infiltrated (and if desired, B-staged), but before
cure and solidification of the preform into a solid green body. The
electrical conductors 104 can be placed manually or by automated
means, and if small enough, even co-weaved within a fiber fabric
102. Additionally, the electrical conductors 104 can be modified
(by coatings, for example), either to enhance the signal
propagation, or to prevent them from reacting with the native HTCs
phases, thus avoiding the formation of unwanted phases and
degrading the sensory network performance.
The geometry of the electrical conductors 104 can be selected to
best fit the component shape, mission requirements and environment,
required density of coverage, cost-efficiency, and so forth. The
electrical conductors 104 are located in one embodiment between
each individual ply 102 of the HTC and, context depending, the
electrical conductors 104 might also be highly localized or more
irregularly distributed. In one embodiment, the electrical
conductors 104 extend outside the confines of the component to
allow attachment to an appropriate readout device (for electrical
current, for example).
Generally, refractory types of metals are selected as the
electrical conductors 104. Because of this and inert atmosphere
processing, softening and oxidation during co-processing with the
HTC are not a problem. Rather, it is the possibility of reaction
between the metal of the electrical conductors 104 and one or more
of the native phases forming unwanted compounds and degrading the
performance of the electrical conductors 104 and the HTC itself. As
mentioned earlier, one way to avoid this is to coat the electrical
conductors 104 with a compound with which they are relatively
stable. Another approach is to apply this method to HTCs that use
native phases that are non-reactive with the chosen metal.
The native phase modification can be achieved in several ways,
depending on the phase chosen for modification. If the matrix 106
is selected, this can be obtained by modifying the polymer (or
using an entirely different polymer) used to create the matrix 106,
and selectively infiltrating a small continuous volume of the
two-dimensional fiber preform, for example a thin strip along the
length of the fabric 102. After this pseudo-infiltration, each
individual, partially-infiltrated ply 102 is cured, then the
infiltration is repeated with the non-modified polymer, this time
filling the rest of the fabric 102 in that same manner. This can be
done individually to each ply 102, or cumulatively if the whole
lay-up 100 is infiltration at once. After cure, the resulting green
HTC will have a pre-determined matrix volume content 112 with
properties that are different from the rest of the matrix 106. In
this case, separate leads can be connected to the modified areas
112 of the lay-up 100 in order to connect them to the appropriate
read-out device.
If the fiber 108 is selected for modification, then this can be
achieved by selectively applying a thin coating 110 over the
already present fiber 108 coating (if any), on a portion of the
fibers 108 present in the fiber weave 102. The coating 110 may be
applied by any conventional deposition method, or as a slurry
containing a phase with the desired characteristics. Regardless of
which coating method is chosen, it is performed on the bare fabric
108, or on the fibers themselves before they are woven into a
fabric, prior to infiltration so that the modified coating 110 is
fully deposited before the matrix 106 formation process is
initiated.
After the new coat 110 is formed, the HTC processing continues
along the traditional route. Similar to the previous modifications,
the goal of this is to introduce a continuous phase within the
volume of the HTC, this time running along the surface of the fiber
weave, with properties different than those of the native
constituents. Here, the fibers 108 coated with the modified
composition 110 extend beyond the edges of the component so as to
allow their connection to the respective read-out device.
Thus, the process is designed so that the newly-integrated or
modified native phase retains through the HTC processing the
properties that make it unique with respect to the surrounding
environment, and the ability to transmit a signal. Additionally, no
new, detrimental phases should be formed that affect the
performance of the HTC (whether mechanical or environmental).
This problematic reactivity is potentially expected between the
electrical conductors 104 and the native HTC phases 102 and 106.
For example, the possibility of at least one of carbide and
silicide formation between the refractory metal electrical
conductors 104 (Nb, Mo, W, Re, Ha, Ta, Pt, Zr, Hf, and so forth)
and a carbon or silicon rich matrix 106 might require the
implementation of a barrier coating in some embodiments, to prevent
this from occurring. The concern is similar if the native-phase
modification route is taken--if there is a possibility of reaction
between the native constituents and the newly-introduced polymer
112 or fiber coatings 110 (whether vapor or slurry deposited),
measures specific to the materials selected are taken in some
embodiments to prevent such reactions, in order to retain the
desired properties of the electrical conductors 104.
The electrical conductors 104 can also be formed by other
deposition methods, such as three-dimensional-printing a continuous
conductive grid, for example. A protective, or property-enhancing
coating on the separate phase can be formed by any conventional
method--including without limitation plasma, electron beam, vapor,
slurry, and electrophoretic. If a modified native phase, the
modifications can be anything that changes the composition of the
native phase, so that it acquires properties different than those
of its native state. Modifying the matrix 106 forming polymer by
adding solid particulates, mixing that polymer with one or more
different polymers, using a completely different polymer, or using
a native polymer with modified composition, are all variations of
the basic approach.
If using reactive melt infiltration, a certain volume 112 of the
preform can be of a composition that is different than the rest, so
that upon infiltration with the liquid material, the required new
phase can be formed only at these locations. The second aspect of
the native-phase modification route (changing the fiber 108 or
coating 110 of the matrix 106), can also be obtained by any of the
conventional deposition methods.
The electrical conductors 104 geometry can be one-dimensional
continuous (for direct readings), or discontinuous (for indirect
readings such as induction-based measurements), two-dimensional and
three-dimensional sensors, continuous or discontinuous, oriented
through-thickness or parallel to the fiber weave direction, can
also be integrated to provide additional functionality, or fit the
geometry of a specific component or need. The native fiber
composition can be carbon, refractory non-oxide or refractory oxide
ceramic, and can be shaped in various orientations (1, 2, 2.5 or
3-dimensional geometries). The matrix 106 can be carbon, refractory
non-oxide or oxide ceramic, and can be obtained by various
processing methods. Polymer infiltration and pyrolysis, (reactive)
melt infiltration, chemical vapor deposition, slurry-based
infiltration, or any combination of these.
As long as it results in an integrated sensor network within the
HTC component, the ordering of the sensor integration and HTC
processing steps (sensor introduction, infiltration, cure,
pyrolysis, and so forth) is not limited to a specific single
sequence.
One use of the various embodiments according to the present
invention is to detect structural and compositional degradation in
HTCs that are subjected to extreme environments. However, the
electrical conductors 104 can also be used for in-situ data
collection from the component and its environment, ex-situ
structural and compositional evaluation of HTC components,
evaluation of processing and fabrication methods for HTCs, impact
detection--localized and widespread, and signal reception and
transmission.
Another embodiment of the invention involves variability in the
forming of the metallic substructure. For certain applications
(communications or directed energy protection, for example), more
complex shapes and morphologies of the electrical conductors 104
might be desirable, that might not be achievable by using long,
straight, wire-like elements. There are a variety of
additive-manufacturing-based methods that can realize this, two
examples being printing patterns with metallic-based inks, or
selectively laser-sintering metallic powders in certain geometries
onto the plies.
While fabric 102 consisting of woven ceramic fibers 108 is one
optional means of reinforcement, the fibrous pre-form 100 can be in
a variety of shapes and still accommodate the invention. For
example, unidirectional tape layup is a fiber architecture-based
processing method that is commonly used in the manufacturing of
HTCs, and is very amenable to the incorporation of the electrical
conductors 104 as proposed. Similarly, three-dimensional preforms
that allow for the manufacture of considerably thicker HTCs are
also amenable to the incorporation of the proposed invention.
Embodiment of the invention can also be implemented to allow
ex-situ inspections of the HTCs, with the integration of the
engineered metallic substructure, which permits non-contact (and
non-destructive) inspection such as by electrical or magnetic means
(such as an eddy current sensor), and to which pure ceramics or
carbon composites are not susceptible. In this manner, the
integrity of the electrical conductors 104 is inspected, and from
there information about the state of the component around that
phase (the rest of the HTC) is inferred. In one embodiment the
electrical conductors 104 do not need to extend to the edges of the
lay-up 100, but are distributed throughout the volume of the HTC.
While the in-situ aspect may be useful from an operational
perspective, the ex-situ option may be useful for long-term
maintenance, and life-cycle considerations.
The foregoing description of embodiments for this invention has
been presented for purposes of illustration and description. It is
not intended to be exhaustive or to limit the invention to the
precise form disclosed. Obvious modifications or variations are
possible in light of the above teachings. The embodiments are
chosen and described in an effort to provide illustrations of the
principles of the invention and its practical application, and to
thereby enable one of ordinary skill in the art to utilize the
invention in various embodiments and with various modifications as
are suited to the particular use contemplated. All such
modifications and variations are within the scope of the invention
as determined by the appended claims when interpreted in accordance
with the breadth to which they are fairly, legally, and equitably
entitled.
REFERENCE NUMBER INDEX
100 Lay-up 102 Ply 104 Electrical conductor 106 Matrix 108 Fiber
110 Electrically conductive coating 112 Electrically conductive
matrix
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